The viaduct on Western and Belmont, which was recently demolished, was initially built to alleviate the traffic back when the Riverview Amusement Park was still there, it closed in 1967. The project seems to be in its second phase, so if you thought the traffic was bad then, you should probably do your best to avoid that intersection for the next 12-16 weeks.
Here’s a piece by Patty Wetli on dnainfo that explains everything you need to know about the construction and where to expect delays.